This invention relates to improved wheel suspension systems for motor vehicles.
A wheel suspension is known from German Patent Document DE 36 16 005 C2 in which a lower transverse control arm is swivellably connected by means of its one end to the vehicle frame and is swivellably connected by means of its other end to a steering knuckle. A strut, which extends approximately in the longitudinal direction, is connected with the transverse control arm, the free end of this strut being elastically supported on the vehicle body.
Furthermore, a wheel suspension is known from German Patent Document DE 32 00 855 A1 in which a strut is connected in an articulated manner with a transverse control arm.
Also, from German Patent Document DE-41 08 164 C2, a wheel suspension is known in which the upper link plane comprises two separated control arms.
It is an object of the invention to provide a wheel suspension for an axle of a motor vehicle which, when peripheral and lateral forces act upon the wheel, ensures a targeted elastokinematic wheel position change which assures stable vehicle handling during cornering and straight-ahead driving.
These objects are achieved according to preferred embodiments of the invention by providing a wheel suspension system comprising:
a wheel carrier for carrying a wheel rotatable about a wheel spin axis and drivingly connected to a wheel drive shaft, PA1 a steering gear tie rod connected to the wheel carrier, PA1 a transverse control arm connected to the wheel carrier by a first joint connection and to a vehicle frame by a second joint connection, PA1 a tension strut connected pivotably to the transverse control arm by a third joint connection and to a vehicle frame by a fourth joint connection, and PA1 an upper wheel carrier support assembly connected to the wheel carrier and to a vehicle frame, said first joint connection and a pole of the connection of the upper wheel carrier support assembly to the vehicle frame defining a control axis, PA1 wherein the transverse control arm with the connected tension strut is arranged below the wheel drive shaft and in front of the tie rod with respect to the driving direction of the vehicle, PA1 wherein the tension strut extends forwardly, diagonally inwardly toward a vehicle center line, PA1 wherein the transverse control arm and the tie rod have a positive adjustment with respect to one another resulting in a wheel steering pole which is situated outside a vehicle wheel track width and behind a wheel center transverse plane, and PA1 wherein the control axis intersects a wheel road surface contact plane at a position in front of the wheel center transverse plane.
The invention is based on two constructions, in which case one construction has a McPherson rear axle and the other construction has two separated control arms instead of the McPherson spring strut. The lower plane of the wheel suspension comprising the transverse control arm, the tension strut and the tie rod has essentially the same design in both constructions.
As a result of the upper plane of the wheel suspension which consists of separated control arms, the so-called imaginary control axis, which forms a point of intersection in the wheel contact plane, for achieving forces acting upon the wheel in the case of braking forces, lateral forces and impact forces, may be designed or adapted in an advantageous manner corresponding to the requirements with respect to the vehicle handling.
The principal advantages achieved by means of the invention are that, as a result of the geometric position of the transverse control arm forming the rear wheel suspension with the connected tension strut and the tie rod, when forces, such as driving, braking and lateral forces act upon the wheel, as well as during load changing operations, a stable vehicle handling is achieved by an elastokinematic adjustment of the wheels. Particularly during cornering, an improvement of the vehicle handling is achieved when a cornering is initiated and when curves change by means of the fact that the wheel on the outside of the curve moves to the toe-in position. In addition, the directional control during braking in a curve as well as during straight-ahead driving is improved as a result of the fact that the rear wheels move into the toe-in position. During an acceleration in a curve, an understeering action of the motor vehicle is usually reinforced. This understeering tendency is reduced by the fact that the rear wheels move into the toe-out position. Furthermore, as a result of this function, when the accelerator is released (load change), the wheel is adjusted in the toe-in direction and, during a load change in a curve, a turning-in is therefore counteracted.
The geometric position of the wheel suspension elements, such as the spring strut, the transverse control arm, the tie rod and the tension strut is particularly selected such that, during the corresponding driving conditions, a targeted moving into the toe-in position or into the toe-out position of the wheel is in each case achieved in an elastokinematic manner.
Thus, when lateral forces act upon the wheel, a toe-in adjustment takes place, particularly of the wheel which is on the outside of the curve. This is achieved by a corresponding design of the caster offset. An axis, which extends through the upper support bearing of the McPherson strut and the pivotal connecting point of the transverse control arm on the wheel carrier, forms a point of intersection in the wheel contact plane--with respect to the driving direction--in front of the direction of the effect of the lateral force. A lever arm is created between the point of intersection and the lateral force. As a result of a moment formed by this lever arm and the lateral force, the tie rod receives a slight pressure force which is lower than the pressure force upon the transverse control arm. Since the tie rod is disposed on the vehicle body in a harder manner than the transverse control arm, it can yield less toward the interior than the transverse control arm which is disposed on the vehicle body in a softer manner.
The transverse control arm and the tie rod have a positive position with respect to one another and form a wheel steering pole which is situated outside the track width and behind the wheel center transverse plane--viewed with respect to the driving direction.
In the case of lateral forces, a moment formed by the lateral force and a lever arm from the wheel steering pole to the direction of the effect of the lateral force is superimposed on the moment resulting from the caster offset.
When the characteristics of the bearings of the tie rod and of the transverse control arm have approximately the same hardness and the bearing of the tension strut on the vehicle body yields in the axial direction, a toe-in of the wheel can occur as a result of the moment formed by the lateral force and the lever arm to the wheel steering pole. In this case, the transverse strut and the tie rod are swivelled toward the rear--with respect to the driving direction--about the body-side bearings, the tension strut also being pulled toward the rear.
In the case of a McPherson rear axle, during the braking of the vehicle, moments are exercised on the wheel which complement one another, on the one hand, by the forming of the wheel steering pole and, on the other hand, by the steering offset, which moments both cause an adjustment of the wheels in the toe-in direction.
For this purpose, the transverse control arm and the tie rod are held in correspondingly coordinated bearings on the vehicle body and the tension strut can shift toward the rear--with respect to the driving direction--by way of the body-side bearing. In this case, the transverse control arm is stressed with respect to pressure and the tie rod is stressed with respect to tension, at the same time, swivelling rearward about their body-side bearings. For limiting the toe-in, the body-side bearing of the tension strut is designed by means of a characteristic limiting the tension movement so that the toe-in can be adjusted corresponding to the requirements.
In the case of the construction of the rear axle with an upper link plane consisting of two separated control arms, a control axis is formed which meets the wheel contact plane within the track width and therefore also within the effective direction of the braking. As a result, in the case of braking forces, the wheel is adjusted in the toe-out direction; however, as a result of the simultaneously acting longitudinal springing, the resulting adjustment of the wheel predominates in the toe-in direction about the wheel steering pole so that, in the final effect, a targeted toe-in adjustment can be achieved.
When driving forces act upon the wheel in the case of the McPherson rear axle, the moment about the wheel steering pole is superimposed on the moment which acts at the level of the wheel spin axis and results from the driving force x the lever arm to the axis so that a wheel position change in the toe-in direction by the latter moment is contrasted by a toe-out adjustment by the other moment. In the case of this toe-out adjustment, the tie rod is pulled and the transverse control arm is pressed, whereas, in the case of the toe-in adjustment, the tension strut is pressed and, as a result, is shifted toward the front in the driving direction in its body-side bearing, in which case the transverse control arm and the tie rod also swivel forward about their body-side bearings.
In the case of a construction of a rear axle system with two separated control arms instead of a McPherson strut system, a control axis is formed by the upper link plane which is situated at the level of the wheel spin axis outside a perpendicular wheel center longitudinal plane, and the wheel is adjusted in the toe-out direction by way of the driving force acting at the level of the wheel center or of the wheel drive shaft. This toe-in change is reinforced by the simultaneously occurring longitudinal springing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.